Desulfurization of petroleum coke



Nov. 9, 1954 FLLJE 6A5 To H EAT REcovEzY DQEHEATED I FUEL. GAS Swen-n- ExcEss Ana 1N FOE QAPlD HEAT\NG W. G. REED, JR

DESULFURIZATION OF PETROLEUM COKE Filed Sept. 17, 1949 ZONE OF RAPID HEATING E EL 5 8 FUEL. GAs+Anz IN 'ZoNE OF CONSTANT TEMP.

WATER COOLED 1 JAcxLE-r ZJZLLLam. G. Reecfldn Gav ante r Clbborneg DESULFURIZATION OF PETROLEUM COKE William G. Reed, Jr., Roselle, N. J., assignor to Standard 1 Oil Development Company, a corporation of Delaware Application September 17, 1949, Serial No. 116,287

Claims. 01. 23-2099 The present invention relates to improvements in the coking of heavy residual petroleum oils such as topped or reduced crude and is particularly concerned with a,

method of reducing the sulfur content of raw petroleum coke.

Crude petroleum oil is ordinarily subjected to distillation in order to remove distillable constituents boiling up to about 825 to 850 F. The residual oil or so-called reduced crude which normally represents about 20-30 vol. per cent of the original crude oil is usually subjected to a pyrolytic treatment such as coking orvisbreaking in order to obtain additional quantities of gas oil, a fraction boiling within the range of from about 400 to 850 F. which may be used as a charging stock to catalytic cracking systems to produce high quality motor fuels. The coking operation ordinarily involves preheating the residual oil to coking temperatures in say a tube furnace and then discharging the preheated oil into a coking retort or drum, preferably heat insulated, in which drum the oil undergoes conversion to form gas, gasoline, coke still bottoms and other products including coke. In such an operation, the coke formed deposits as a solid clinging to the bottom and side walls of the drum. Eventually the operation must be discontinued and the coke removed by shutting down the drum, letting the coke {dry and harden and then breaking the coke loose from the drum by mechanical or hydraulic means. It has also been proposed to coke residual oils continuously as by preheating the'residual oil substantially to coking temperatures, reducing the oil to droplets, passing the droplets in free falling condition through a coking section and then through a drying and hardening section where the coke particles are heated by combustion gases to temperatures of 1050 to 1800 F. whereby hard, dry pellets or granules of coke are obtained. It has also been proposed to coke reduced crudes by discharging the reduced crude preheated to temperatures of about 800 to 850 F. onto coke particles which are preheated to coking temperatures of about 1000 to 1500 F.', whereupon the coke particles maybe heated to temperatures of about 1400 to 1800 F. to dry the same or drive off-further amounts of-volatilizable materials from the resulting petroleumcoke.

these processes contains from about 3 to 5 wt. per cent of sulfur. Because of this high sulfur content petroleum coke is incapable of meeting certain specifications for metallurgical purposes and for electrode manufacture and is therefore only assigned fuel value in economic analyses of reduced crude coking processes. If the sulfur content were reduced to about 1 to 1 /2 per cent, or, at least, no more than 2 per cent, the coke would be suitable for metallurgical purposes and electrode manufacture and would therefore command a substantially higher price than ordinary petroleum coke.

It is the object of this invention to reduce the sulfur content of petroleum coke to such an extent as to render it suitable for metallurgical purposes or electrode manufacture.

It is also an object of this invention to prepare petro-' It has been found that it is feasible to reduce the Petroleumcoke produced from most crude oils by sulfur content of petroleum fuel may be sulfurizing vessel lC C coke by subjecting the same to a severe thermal treatment. It has been found that this heat treatment is most eifective if the heating of the coke to desulfurization temperature is accomplished in a very short period of time. The purpose of this rapid shock heating to desulfurizing temperatures, i. e.,

to-2500 to 3200 F., or preferably at 2500 to 2700 F,

is to drive off a maximum amount of sulfur while 'it is in adsorbed or easily removable form: It is believed that slow heating of the sulfur-containing coke tends to change the sulfur from .the adsorbed form into the solid solution form, a much less readily evolved form. This thermal, treatment can be accomplished in a batch operation or preferably in a moving bed process wherein necessary heat is supplied by combustion of part of the charge or by combustion of an extraneous fuel within the bed.

process.

In the drawing, coke particles that vided with a bell closure 11 or the like for controlling the discharge of coke particles from the hopper. Ade- 12 is arranged below the hopper 10,

10 is a hopper for holding the raw the bellclosure escape of gaseous materials from vessel 12 into hopper 10. Inlets 13 are arranged in the upper part of vessel 12 for the supply of fuel gas containing preferably a slight excess of'air and preferably preheated in order to create a zone of rapid heating at the upper part of the vessel 12.

The excess air introduced at 13 may serve to partially burn the coke particles in order to raise them rapidly to the active desulfurizing temperatures of 2500 to 3200 F. If desired, radiant heating means may be arranged inside the upper part of the vessel 12 in order to insure the maintenance of this upper part of the vessel at 2500 to 3200 F. Additional inlets 14 are arranged in vertically spaced relation in thewalls of vessel 12 .:-in order to supply fuel gas and air in sufficient amount if this is necessary to maintain a zone of essentially constant temperature within the range of 2500 to 3200 F for a period of time sufficient to attain the desired sulfurizing action. Gases supplied to and evolved. in vessel 12 are withdrawn from the top of the Vessel through outlet line 15 and passed through suitable heat recoveryv equipment. Flow of desulfurized coke from the vessel 12 is controlled by slide valve 16 or the like arranged at the bottom of the vessel. the temperature of the coke as discharged from the vessel 12 a jacket 17 is arranged around the bottom portion of the vessel 12 as well as the valve 16 through which a suitable cooling agent such as water circulated. Indirect heat exchange with feed air and a preferable means of reducing the temperature of the coke. The desulfurized coke is discharged from the bottom of vessel 12 into a vessel 18 which may contain a quenching acid solution if it is desired to wash out some of the ash-forming constituents from the coke.

The operation of this apparatus is as follows: Raw petroleum coke containing from 3 to 6 wt. per cent of sulfur produced in any desired coking operation is supplied to hopper 10 in the form of lumps or granules. It is preferred that the particles of coke be small enough to pass about a 2 mesh screen. tinuously or intermittently to reactor 12. Fuel gas plus a small amount of excess air, preferably preheated, is supplied through inlets 13 at the top of the reaction heated to active desulfurization temperatures whereby amaximum amount of adsorbed and relatively easily removable sulfur is driven off'before it can be converted to the solid solution form in which it is more tenaciously held by the coke particles. Further amounts of fuel gas l atented Nov. 9, 1954 in the single figure, a suitare to be treated and which is pr0-' member 11 serving also to prevent the In order to regulate y be.

liquid such as water or a dilute Coke is supplied conand air are supplied, if necessary, to the body of the reaction vessel 12 in order to maintain the coke particles at temperatures within the range of 2500 to 3200 F. for a substantial portion of its travel through the vessel. This gas not only serves to maintain the coke at; desuifurization temperatures but also provides a carrying gas for the sulfur driven out of the coke particles. The time of residence of the coke particles at temperatures Within the range of 2500 to 3200 F. may vary from about tto about 6 or 8 hours, depending to a great extent upon the particle size of the coke and the source of the coke. Lumps about one inch in diameter may require about 6 to' 8 houis at 2500 to 3200 F. in order to reduce the sulfur content.

The following example is illustrative of the present invention:

A graphite crucible about 3 /2 inches high and about 2% inches in' diameter was placed in the bottom of a quartz tube 3' inches in diameter and 12 inches long provided with a closure at the top through WhlCh lt was possible to admit a purging gas and from wh ch the evolved gases were released. Insulating. material was arranged between the bottom and side of the quartz tube and the graphite crucible and the entire assembly was inserted in a 3 kw. induction furnace. The gen-- eral operating procedure consisted of introducing the coke charge into the crucible, starting the purge gas and applying the electric current for the desiredperrod of time. The coke charge was not itself appreciably heated inductively by the electric field but indirectly from the heat generated in the graphite crucible by the electric field. The coke heated very rapidly and was up to the maximum temperature, approximately 2700 F., in .1 few minutes. The temperature to which the coke was heated was determined by removing the top of the quartz tube momentarily, sighting on the coke with an optical pyrometer and correcting the readings so obtained for the emissivity of the coke.

Petroleum coke obtained by spraying a reduced West Texas crude upon coke particles at temperatures of about 1000 to 1200 F. and containing 5 wt. per cent sulfur was desulfurized in the above equipment. The results obtained on various fractions of the coke ranging in size from I mesh down to 60-100 mesh are summarized in the table.

These tests indicate that about half the sulfur initially present in the 60-100 mesh material is evolved in a few minutes and within 4 hours sulfur content 18 less than 1%. The sulfur content of 1 mesh lump coke is reduced more slowly and extrapolation of the data suggests that 6-8 hours might be required to reach 1% sulfur.

The foregoing description contains a limited number of embodiments of the present invention. It will be understood, however, that numerous variations are possible' without departing from the scope of the fOHOWIIIg claims. 7

What is claimed is:

1. The method of reducing. the sulfur content of raw petroleum coke containing 3 to 6 weight per cent sulfur and prepared by heating high sulfur-content residual petroleum oil at a coking temperature of up to 1800 R, which comprises introducing the raw coke into a terminal part of an elongated desulfurizing zone maintained at a desulfurizing temperature in the range between about 2500 and 3200" F., also feeding an oxygen-containing gas directly into the terminal part of the desulfurizing zone which contains the freshly introduced coke, whereby the fresh coke feed is rapidly heated to the said desulfurizing temperature, passing the coke through the desulfurizing zone, maintaining the coke at the desulfurizing temperature for a period between about Me and 8 hours until the content of the coke is reduced below 2 weight per cent, and withdrawing a sulfur-containing gas and desulfurized coke from the desulfurizing zone.

2. The method of reducing the sulfur content of raw petroleum core containing 3 to 6 weight per cent sulfur and prepared by heating high sulfur-content residual petroleum oil at a coking temperature of up to 1800 F. which comprises introducing particles of raw coke ranging in size between about 1 and mesh into the top part of an elongated, substantially vertical desulfurizing zone onto a bed of coke particles maintained at adesulfurizing' temperature in the range between 2500' and 3200 F., also feeding a preheated fuel gas and a slight excess of air into the top part of the desulfurizing zone containing the freshly introduced coke, whereby the fresh coke feed is rapidly heated to the desulfurizing temperature, passing the coke particles downwardly through the desulfurizing zone, supplying further fuel gas and air to lower parts of the desulfurizing zone in order to maintain the coke at the desulfurizing temperature, removing a sulfur-containing gas from an upper portion of the desulfurizing zone, maintaining the coke particles at the high temperature in the desulfurizing zone for a period between A and 8 hours until their sulfur content is re} duced below 1.5 wt. per cent, cooling the resulting'desulfurized coke and removing it from a bottom portion of the desulfurizing zone. p

3. A method according to claim 2 wherein the desulzone is maintained between about 2500 and 4. The method of reducing the sulfur content of petroleum coke prepared by heating high sulfur-content residual petroleum oil at a coking temperature of up to- 1800 R, which comprises introducing petroleum coke particles of a particle size of about 60 to 100 mesh and a sulfur content of about 3 to 6 weight per cent into the top part of a desulfurizing zone maintained at a desulfurizing temperature in the range between 2500 and 2700" F.,- also feeding air into the top part of the desulfurizing zone to heat the freshly introduced coke rapidly to a temperature within the aforesaid range, sup' plying further air to lower parts of the desulfurizing zone to maintain the desired temperature, passing the coke particles downwardly while maintaining" them at the desulfurizing temperature for about 4 hours and thereby reducing the sulfur content of the coke to, less than 2 wt. per cent, cooling and withdrawing the desul= furized coke including volatilizable materials from a bottom part of the desulfurizing zone, and separately withdrawing a sulfur-containing gas from an upper part of the desulfurizing zone.

5. The method of reducing the sulfur content of petroleum coke prepared by heating high sulfur-content residual petroleum oil at a coking temperature of up to- 1800 R, which comprises introducing petroleum coke particles of a particle size of about 1 mesh and a sulfu'r content of about 3 to 6 Weight per cent into the top part of a substantially vertical, elongated desulfurizing zone maintained at a desulfurizing temperature in the range between 2500 and about 2700 F., also feed-ing fuel gas and air into the top part of the desulfurizing zone to heat the freshly introduced coke rapidly to the desulfurizing temperature, supplying further amounts of fuel gas andair to lower sections of the desulfurizing zone, passing the coke particles down through the desulfurizing zone whilemaintainmg them at the desulfurizingtemperature for about 6 to 8 hours and thereby reducing the sulfur content of the coke to less than 2 weight per cent, coming and withdrawing the dcsulfurized coke including volatilizable materials from a bottom part of the desulfu ri z1ng zone, and separately withdrawing a sulfur-containmg gas from an upper part of the desulfurizing zone:

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,789,380 Edwards et al. Ian. 20, 1931- 2,201,050 Oberle May 14', 1940 2,260,746 Hanawalt et al. Oct. 28, 1 94] 2,342,862 Hemminger Feb. 29, 1944 OTHER REFERENCES Petroleum Processing, March 1952, pages 351-352. 

1. THE METHOD OF REDUCING THE SULFUR CONTENT OF RAW PETROLEUM COKE CONTAINING 3 TO 6 WEIGHT PER CENT SULFUR AND PREPARED BY HEATING SULFUR-CONTENT RESIDUAL PETROLEUM OIL AT A COKING TEMPERATURE OF UP TO 1800* F., WHICH COMPRISES INTRODUCING THE RAW COKE INTO A TERMINAL PART OF AN ELONGATED DESULFURIZING ZONE MAINTAINED AT A DESULFURIZING TEMPERATURE IN THE RANGE BETWEEN ABOUT 2500* AND 3200* F., ALSO FEEDING AN OXYGEN-CONTAINING GAS DIRECTLY INTO THE TERMINAL PART OF THE DESULFURIZING ZONE WHICH CONTAINS THE FRESHLY INTRODUCED COKE, WHEREBY THE FRESH COKE FEED IS RAPIDLY HEATED TO THE SAID DESULFURIZING TEMPERATURE, PASSING THE COKE THROUGH THE DESULFURIZING ZONE, MAINTAINING THE COKE AT THE DESULFURIZING TEMPERATURE FOR A PERIOD BETWEEN ABOUT 1/4 AND 8 HOURS UNTIL THE CONTENT OF THE COKE IS REDUCED BELOW 2 WEIGHT PER CENT, AND WITHDRAWING A SULFUR-CONTAINING GAS AND DESULFURIZED COKE FROM THE DESULFURIZING ZONE. 